BEYOND study is designed to generate the first real-world data from GCC countries on the patient characteristics, treatment patterns, survival outcomes, and safety of T-DXd in patients with HRpositive,HER2-low or HER2-ultralow mBC previously treated with ET. The evidence generated will help to optimise treatment strategies, inform clinical guidelines, and ultimately improve outcomes for patients with mBC across the region.

Inclusion Criteria:

• -Female patients aged ≥18 years old at the time of T-DXd initiation
• Patients with a confirmed histological or cytologically based diagnosis of HR-positive mBC.
• Patients who were classified as HER2-low or HER2-ultralow mBC confirmed by the closest locally obtained HER2 test prior to or on the index date, and who meet the following definitions:
• HER2-low status defined as IHC scores 1+ and 2+ without ISH gene amplification based on the pathology report.
• HER2-ultralow status defined as IHC 0 with membrane staining based on the pathology report.
• Patient who received at least one prior line of ET (± targeted therapy) in the metastatic setting.
• Patients who are chemotherapy-naïve in the metastatic setting.
• Patients who initiated T-DXd up to 30 days before the signature of the ICF. The decision to initiate T-DXd must be made independently by treating physicians as part of routine clinical practice.
• Patients are willing to sign the written ICF, indicating that they understand the purpose of the study and procedures required for participation.

Exclusion Criteria:

• -Patients with a history of other malignancies, other than basal cell carcinoma of the skin and squamous cell carcinoma of the skin.
• Patients who received prior chemotherapy in the metastatic setting.
• Patients with Eastern Cooperative Oncology Group (ECOG) status ≥2 or missing ECOG status at the time of initiation of T-DXd (index date).
• Patients with a history of participation in another clinical trial in the metastatic setting.
• Female patient with current or planned pregnancy, or breastfeeding.

Female patients aged ≥18 years old at the time of T-DXd initiation

The study population will consist of adult (age ≥ 18 years old at the date of T-DXd initiation) female patients with a confirmed diagnosis of HR-positive, HER2-low (defined as immunohistochemistry [IHC] 1+ or IHC 2+/In situ hybridization [ISH]-) or HER2-ultralow (IHC 0 with membrane staining) mBC that has progressed on one or more ET in the metastatic setting and initiated T-DXd up to 30 days before the index date.

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal Vivli.org. All requests will be evaluated as per the AZ disclosure commitment:

https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure. Yes, indicates that AZ are accepting requests for IPD, but this does not mean all requests will be shared.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA PhRMA Data Sharing Principles. For details of our timelines, please rerefer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure

When a request has been approved AstraZeneca will provide access to the anonymized individual patient-level data via secure research environment Vivli.org.

Signed Data Usage Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information